Merge pull request #153 from ashwek/ms1

Prefix Evaluation - Python

Author: ionicc

Mathematical_Algorithms/src/prefix_evaluation.py

@@ -0,0 +1,52 @@
+"""
+Output:
+
+Enter a Prefix Equation (space separated) = + 8 ^ 6 2
+ Symbol  |    Action    | Stack
+-----------------------------------
+       2 | push(2)      | 2
+       6 | push(6)      | 2,6
+         | pop(6)       | 2
+         | pop(2)       |
+       ^ | push(2^6)    | 64
+       8 | push(8)      | 64,8
+         | pop(8)       | 64
+         | pop(64)      |
+       + | push(64+8)   | 72
+
+	Result =  72
+"""
+
+import operator as op
+
+def Solve(Postfix):
+    Stack = []
+    Div = lambda x, y: int(x/y)     # integer division operation
+    Opr = {'^':op.pow, '*':op.mul, '/':Div, '+':op.add, '-':op.sub}     # operators & their respective operation
+
+    # print table header
+    print('Symbol'.center(8), 'Action'.center(12), 'Stack', sep = " | ")
+    print('-'*(30+len(Postfix)))
+
+    for x in Postfix:
+        if( x.isdigit() ):          # if x in digit
+            Stack.append(x)         # append x to stack
+            print(x.rjust(8), ('push('+x+')').ljust(12), ','.join(Stack), sep = " | ")      # output in tabular format
+        else:
+            B = Stack.pop()             # pop stack
+            print("".rjust(8), ('pop('+B+')').ljust(12), ','.join(Stack), sep = " | ")      # output in tabular format
+
+            A = Stack.pop()             # pop stack
+            print("".rjust(8), ('pop('+A+')').ljust(12), ','.join(Stack), sep = " | ")      # output in tabular format
+
+            Stack.append( str(Opr[x](int(A), int(B))) )         # evaluate the 2 values poped from stack & push result to stack
+            print(x.rjust(8), ('push('+A+x+B+')').ljust(12), ','.join(Stack), sep = " | ")      # output in tabular format
+
+    return int(Stack[0])
+
+def Convert(Prefix):
+    Prefix.reverse()        # Reverse  the Prefix Equation
+    return Solve(Prefix)    # evaluate the reversed Prefix Equation (as a Postfix Equation)
+
+Prefix = input("\n\nEnter a Prefix Equation (space separated) = ").strip().split(' ')
+print("\n\tResult = ", Convert(Prefix))